ok so im a girl, and my boyfriend always does this..in school when im talking to my friends he creeps up behind me and grabs me by the waist and hugs me from behind..ahhh it makes me want him more and more each time!!!

but before you do this please make sure that she actually likes you and if your not sure if she does start from a small flirt to bigger and bigger untill you get to the kiss.
It works everytime! trust me!
Good Luck